base

Added the subset of partial content support so that
we can continue the interrupted request to support
streaming the content even with a brief disconnection.

Note: we don't update the headers for partial content
as the headers we care should not be updated. See
a list in chromium/net/http/http_response_headers.cc.

We currently also don't support cache for partial content.

Fix http://b/issue?id=2616477